1. Field of the Invention
The present invention relates to a negative pattern-forming material for the purpose of forming highly accurate patterns in desired configurations on a substrate. In particular, the present invention relates to a pattern-forming material which is ideal as a mask highly resistant to the dry etching of an underlying organic material, for example, an organic insulating material or an organic planarizing layer as used in multilayer resist methods, as encountered in, for example, microprocesses in the fabrication of semiconductor devices. The present invention also relates to a pattern formation method which uses the aforesaid pattern-forming material.
2. Background Information
According to current trends toward higher densities in semiconductor devices, for example, in IC's and LSI's, both a microminiaturization of unit elements and a reduction in pattern line widths are underway, and submicron patterns will be entering into the stage of practical utilization. With regard to the formation of the corresponding micropatterns, within the field of photolithography attention has been directed at lithography using, for example, deep UV, electron beams, and X-rays, as exposure sources having excellent short-time resolving powers among the various wavelengths. In order to form high-resolution high-aspect ratio resist micropatterns using this type of lithography, the resist film must be thin and must also have a uniform thickness in order to minimize effects such as, for example, backscatter from the substrate and forward scatter. However, as in the case when circuitry has already been formed prior to such a resist coating, or in the case of the formation of multilayer circuitry or elements with a three-dimensional array structure, among others, the substrate on which the resist pattern must be formed is often not flat, and it is very difficult to form thin, defect-free (e.g., without pinholes, etc.) resist layers on such substrates. Furthermore, when the resist surface is not flat as a consequence of substrate topography, effects such as a variable electron beam dosage and scatter readily occur, and it becomes difficult to direct the process toward the formation of a micropattern with the desired layout. This makes it necessary to increase the film thickness in order to planarize the resist surface. Furthermore, a too thin resist film is undesirable from the standpoint of its resistance to dry etching, which has recently entered into widespread use.
Multilayer resist strategies have been proposed in order to meet these conflicting demands. For example, in a trilayer structure, the substrate is planarized by a first layer of an organic polymer, and this is covered with an intermediate layer of an inorganic material which is highly resistant to oxygen ion etching, for example, a silicon dioxide film or vapor-deposited metal film. On this is then formed a thin resist layer. It is this resist layer which is patterned by exposure and development, and the obtained resist pattern is then used as a mask for processing of the intermediate layer by dry etching. The image patterned into the intermediate layer is then used as a mask for the processing of the thick organic polymer first layer by oxygen ion etching, thus finally providing a micropattern on the substrate. The third layer, the resist layer, is removed during the ion etch.
With regard to the advantages of this trilayer resist approach, it becomes possible to obtain an ultramicrofine pattern through the use of a thin resist third layer, and the use of a highly dry etch-resistant organic polymer layer as the first layer makes it possible to obtain a highly dry etch-resistant resist film.
However, this methodology has the disadvantage of substantially increasing the number of processes. A bilayer resist strategy has been proposed in response to this. In the bilayer resist approach, a thin resist layer is placed on an organic polymer layer. After formation of a resist pattern, it is used as a mask for etching the organic polymer using an oxygen plasma. Thus, in a bilayer resist, the upper resist layer must have a fairly good oxygen plasma resistance, that is, resistance to oxygen ion etching, at the same time that it has a high sensitivity and high resolvability. Resist materials having a good oxygen ion-etch resistance have been proposed in the form of silicon-containing polymers into which highly sensitive groups have been introduced as described by Nippon Electric KK in Japanese Patent Application Laid Open [Kokai or Unexamined] Numbers 58-207041 [ 207,041/83], published Dec. 2, 1983; by Nippon Telegraph and Telephone in Japanese Laid Open Application No. 60-212756 [ 212,756/85], published Oct. 25, 1985; and by Nippon Telegraph and Telephone in Japanese Laid Open Application No. 61-20032 [ 20,032/86]), published Jan. 28, 1986.